1. Field of the Invention
The present invention relates to techniques for processing video signals, such as are used in systems for image acquisition, in particular in the sector of consumer-electronics devices, that acquire images by means of digital sensors, such as CCDs or CMOS sensors, including reduced size color displays, and corresponding computer program.
2. Description of the Related Art
In the applications to which reference has been made above, the input data are normally acquired according to a Bayer configuration or pattern (see in this connection U.S. Pat. No. 3,971,065). To obtain the final image it is necessary to apply a reconstruction algorithm, the purpose of which is to exploit as far as possible the information acquired by the sensor to obtain the best possible image. For a general discussion of the problems linked to this approach, useful reference may be made to the work of M. Mancuso and S. Battiato: “An introduction to the digital still camera technology”, ST Journal of System Research, Vol. 2, No. 2, pp. 1-9, December, 2001.
The block diagram of FIG. 1 represents the typical configuration of the image-acquisition system present, for example, in a digital videocamera or still camera of general production.
The reference number 10 designates the image sensor, i.e., the physical sensor (for example, CCD/CMOS).
The corresponding output signal is usually organized according to a Bayer pattern of the type presented in FIG. 2.
The information contained in this type of image corresponds to a sub-sampling of a color image. In the pattern, each pixel contains information regarding just one color “channel” (red, green, blue). All the color channels regarding a pixel can be reconstructed by means of interpolation of the information regarding the individual channels.
The reference number 12 in the diagram of FIG. 1 designates a module that performs a pre-processing of the data supplied by the sensor 10 with a view to subsequent treatments. In particular, comprised in this module are a block for white balancing, a block for construction of the color matrix, a block for range correction, etc.
The block 14 performs the reconstruction of the color image from the Bayer pattern. The corresponding output is represented by an image in which the chromatic information has been reconstructed, i.e., in which each pixel has the information regarding each channel, and the missing information has been reconstructed by the module 14.
The corresponding image signal can then be transferred to a module 16 functioning as a compression module (typically according to the JPEG standard) with a view to storage in a memory 18. The memory in question can be constituted either by the physical medium on which the video signals are stored (videocassettes, CD-ROMs, etc.) or by a memory associated to a display unit (not illustrated).
In the case of a videocamera or similar device (e.g., digital still camera) the signal at output from the sensor 10 is supplied—in addition to the “main” processing chain illustrated previously—also to an auxiliary processing chain having the function of processing an image designed to be presented on a viewfinder that enables the user to recognize the characteristics of the image that he is photographing.
For the above purpose, the signal arriving from the sensor 10 is supplied to a module designated by 20 which processes it in such a way as to enable presentation of the signal on a display or viewfinder designated by 22.
The corresponding refresh factor must be sufficiently high to cause the image presented on the viewfinder to correspond effectively to the images photographed of filmed and treated by the main processing chain comprising the elements designated by 12 to 18.
The viewfinder 22 must therefore present a somewhat high refresh rate (frame rate), but the image presented need not have a very high quality, since it primarily has the purpose of functioning as preview of the final image, interpolated as much as possible.
At the same time it is important that the image presented on the viewfinder 22 should provide a sufficiently faithful representation of the characteristics of the image proper in terms of color balancing and construction of the corresponding matrix. However, since in the final analysis it is an auxiliary or additional function, it is desirable to proceed so that the function of processing implemented in the module 20 is not excessively burdensome from the computational standpoint or from the standpoint of circuit complexity or both.